1. Field of the Invention
The present invention relates to a gas-liquid separator for separating a gas-liquid two-phase flow into a gas and a liquid. Such gas-liquid two-phase flow is generated from an apparatus using a liquid, such as a polishing apparatus for polishing a substrate surface while supplying a polishing liquid onto a polishing surface. The present invention also relates to a polishing apparatus provided with such a gas-liquid separator.
2. Description of the Related Art
In a polishing apparatus which polishes a substrate surface while supplying a polishing liquid to a polishing surface, a gas-liquid two-phase flow is generated which is constituted by a polishing liquid, containing polishing agent and polishing abrasives therein, and a gas, such as nitrogen gas, supplied during polishing or cleaning of the substrate. Such a gas-liquid two-phase flow may be generated as a result of mixture of a waste cleaning liquid, used in cleaning of the polishing surface, and the gas such as nitrogen gas, or may be generated when a gas is mixed into the polishing liquid or the waste cleaning liquid.
In order to prevent such a gas-liquid two-phase flow from flowing into an exhaust line and causing clogging of the exhaust line with the liquid, it is common practice in a polishing apparatus to provide a gas-liquid separator for separating the gas-liquid two-phase flow into a gas and a liquid and discharging them.
FIG. 1 is a vertical cross-sectional front view showing an example of a conventional gas-liquid separator. As shown in FIG. 1, the gas-liquid separator includes a cylindrical separator body 100 with an open top and a closed bottom, and a gas-liquid introduction pipe 104 for introducing a gas-liquid two-phase flow, which has been generated on a polishing table (not shown) or the like and recovered by a drain receiver 102, into the separator body 100. The gas-liquid introduction pipe 104 is coupled to a lower end of a connecting pipe 106 and extends downward. The connecting pipe 106 is connected to a bottom of the drain receiver 102 and extends vertically. The gas-liquid introduction pipe 104 has its lower end located near the bottom of the separator body 100. The bottom of the separator body 100 is provided with a liquid discharge outlet 100a communicating with a drain pipe 108. A side portion of the separator body 100 is provided with a gas discharge outlet 100b communicating with an exhaust pipe 110. This gas discharge outlet 100b is located at a position above the lower end of the gas-liquid introduction pipe 104.
The gas-liquid two-phase flow, recovered in the drain receiver 102, flows through the gas-liquid introduction pipe 104 and is introduced into the interior of the separator body 100. The liquid, which has been separated from the gas-liquid two-phase flow and collected on the bottom of the separator body 100, is discharged through the liquid discharge outlet 100a and the drain pipe 108. The gas, which has been separated from the gas-liquid two-phase flow and has ascended to the upper portion of the separator body 100, is discharged through the gas discharge outlet 100b and the exhaust pipe 110.
In order to prevent the gas-liquid two-phase flow in the gas-liquid introduction pipe 104 from flowing into the exhaust pipe 110, the lower end of the gas-liquid introduction pipe 104 has a tapered portion (cutout portion) 104a on the opposite side from the exhaust pipe 110 (the side not facing the exhaust pipe 110).
There has been proposed a waste liquid and waste gas treatment apparatus which, in order to efficiently discharge mist of polishing liquid generated during polishing, simultaneously collects a polishing liquid and mist of polishing liquid in a drain receiver, and introduces the mixture into a gas-liquid separation means through a common discharge pipe to separate the mixture into a waste liquid and a waste gas and discharge them (see Japanese Patent Laid-Open Publication No. H10-123336). There has also been proposed a gas-liquid separator which has a housing for storing a liquid discharged from a liquid discharge section of a separator body. This housing is provided with a liquid discharge outlet and a gas discharge outlet (see Japanese Patent Laid-Open Publication No. 2008-38712 and Japanese Patent Laid-Open Publication No. 2008-38714). Further, there has been proposed a gas-liquid separator which has a spiral plate installed in a tubular nozzle for introducing a gas-liquid mixture into a tank (see Japanese Utility Model Laid-Open Publication No. S62-109709).
The gas-liquid separator shown in FIG. 1 has the advantage that it has relatively compact structure and is suitable for installation e.g. at a bottom of a polishing apparatus. However, the gas-liquid two-phase flow descends freely in the gas-liquid introduction pipe 104 without any obstructions to impinge on the bottom of the separator body 100 with high impact. Therefore, when a relatively large amount of gas-liquid two-phase flow is treated, a large amount of mist will be produced in the separator body 100. Moreover, if a liquid to be treated contains a foaming material, foaming of the liquid is promoted, resulting in production of a large amount of bubbles in the separator body 100. When a large amount of mist or bubbles is produced, the mist or bubbles may reach the exhaust pipe 110 and the liquid may remain in the exhaust pipe 110, thus causing problems, such as leakage thereof.
Particularly in a polishing apparatus, a polishing liquid containing a foaming additive, such as a dispersant, is used. In addition, a large amount of water and gas, such as nitrogen gas, are used for spray cleaning (atomizer cleaning) after polishing of a substrate. Therefore, a large amount of mist or bubbles is likely to be generated in the separator body 100.
None of the above-described patent documents addresses such a problem of the generation of the mist or bubbles due to collision of the gas-liquid two-phase flow with the bottom of the separator body.